1. Field of Invention
The present invention relates to semiconductor light emitting devices that emit polarized light.
2. Description of Related Art
Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, a light emitting or active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. One class of UV through green light emitting diodes or short wavelength laser diodes use InGaN/GaN or InGaN/InGaN strained quantum wells to generate light by the recombination of electrons and holes injected from the n- and p-type regions sandwiching the quantum wells.
In many III-nitride devices, the crystal structure is wurtzite with two equivalent crystal axes in the plane of the quantum well and a third crystal axis, the <0001> axis, perpendicular to the quantum well. Light emitted from such devices is observed to have no net polarization, meaning that any point (atom, molecule, or electron-hole pair) in the active region of such devices is observed to emit light with a polarization direction randomly and very quickly (typically less than 10 nanoseconds) changing in time so that no net polarization is observed over longer time scales. Such conventional structures are said to emit randomly polarized light.